The girl finds the computer game _____ boring.

The correct choice indicates that the girl finds the computer game excessively dull. The word "it" is used here to refer back to the computer game, which makes the sentence grammatically coherent.

In English, we typically use "find" followed by an adjective to describe our opinions or feelings about something. In this case, the structure "finds the computer game it boring" is syntactically incorrect, as "it" does not function naturally in this context. Instead, the adjective that follows "finds" should directly describe the game.

The other options present alternatives to accentuate the level of boredom. However, they do not fit grammatically in this phrase structure. Words like "too," "so," and "very," all modify the adjective but do not stand alone as subjects in this context. Therefore, while "it" attempts to serve as a subject, it actually disrupts the flow of the sentence, making it unsuitable as a correct response.

In summary, the choice should not be "it" because it does not conform to standard English grammar rules for expressing opinions about a noun through an adjective. Understanding how sentence structure operates is crucial to choosing appropriate responses.